Condensed Consolidated Statement of Shareholders' Equity - USD ($) $ in Thousands	Total	Common Shares [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Treasury Shares [Member]
Shares Outstanding, Beginning Balance at Dec. 31, 2017		27,856,752
Stockholders' Equity, Beginning Balance at Dec. 31, 2017	$ 747,298	$ 295	$ 306,483	$ 473,329	$ (32,809)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	18,063			18,063
Proceeds from issuance of common shares for conversion of convertible notes	20,309	$ 6	20,303
Common shares issued for conversion of convertible notes		628,515
Stock options exercised, shares		24,220
Stock options exercised	426		(56)		482
APIC, Share-based Payment Arrangement, Increase for Cost Recognition	1,039		1,039
Deferral of executive and director compensation	185		185
Executive and director deferred compensation distributions shares		61,366
Executive and director deferred compensation distributions	(955)		(2,174)		1,219
Shares Outstanding, Ending Balance at Mar. 31, 2018		28,570,853
Stockholders' Equity, Ending Balance at Mar. 31, 2018	786,365	$ 301	325,780	491,392	(31,108)
Shares Outstanding, Beginning Balance at Dec. 31, 2017		27,856,752
Stockholders' Equity, Beginning Balance at Dec. 31, 2017	747,298	$ 295	306,483	473,329	(32,809)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	45,974
Shares Outstanding, Ending Balance at Jun. 30, 2018		28,570,853
Stockholders' Equity, Ending Balance at Jun. 30, 2018	815,966	$ 301	327,470	519,303	(31,108)
Shares Outstanding, Beginning Balance at Mar. 31, 2018		28,570,853
Stockholders' Equity, Beginning Balance at Mar. 31, 2018	786,365	$ 301	325,780	491,392	(31,108)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	27,911			27,911
APIC, Share-based Payment Arrangement, Increase for Cost Recognition	1,691		1,691
Deferral of executive and director compensation	(1)		(1)
Shares Outstanding, Ending Balance at Jun. 30, 2018		28,570,853
Stockholders' Equity, Ending Balance at Jun. 30, 2018	815,966	$ 301	327,470	519,303	(31,108)
Shares Outstanding, Beginning Balance at Dec. 31, 2018		27,516,218
Stockholders' Equity, Beginning Balance at Dec. 31, 2018	855,303	$ 301	330,517	580,992	(56,507)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	17,723			17,723
Stock options exercised, shares		136,740
Stock options exercised	2,428		(550)		2,978
APIC, Share-based Payment Arrangement, Increase for Cost Recognition	$ 912		912
Repurchase of Common Shares, shares	200,000	(201,088)
Repurchase of common shares	$ (5,150)				(5,150)
Deferral of executive and director compensation	246		246
Executive and director deferred compensation distributions shares		116,956
Executive and director deferred compensation distributions	0		(2,545)		2,545
Shares Outstanding, Ending Balance at Mar. 31, 2019		27,568,826
Stockholders' Equity, Ending Balance at Mar. 31, 2019	871,462	$ 301	328,580	598,715	(56,134)
Shares Outstanding, Beginning Balance at Dec. 31, 2018		27,516,218
Stockholders' Equity, Beginning Balance at Dec. 31, 2018	855,303	$ 301	330,517	580,992	(56,507)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	47,969
Shares Outstanding, Ending Balance at Jun. 30, 2019		27,617,366
Stockholders' Equity, Ending Balance at Jun. 30, 2019	904,240	$ 301	330,052	628,961	(55,074)
Shares Outstanding, Beginning Balance at Mar. 31, 2019		27,568,826
Stockholders' Equity, Beginning Balance at Mar. 31, 2019	871,462	$ 301	328,580	598,715	(56,134)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	30,246			30,246
Stock options exercised, shares		48,540
Stock options exercised	849		(211)		1,060
APIC, Share-based Payment Arrangement, Increase for Cost Recognition	1,682		1,682
Deferral of executive and director compensation	1		1
Shares Outstanding, Ending Balance at Jun. 30, 2019		27,617,366
Stockholders' Equity, Ending Balance at Jun. 30, 2019	$ 904,240	$ 301	$ 330,052	$ 628,961	$ (55,074)